Battery Overcharge?

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Veteran Member
Nov 20, 2009
United States Of America
Vessel Name
Reef Drifter
Vessel Make
1983, 34 ft., Marine Trader
I noticed some puddles of water on top of one of my two start batteries.** Is this from overcharging?* The boat is not used every day but I do keep the battery charger on when at the dock.* If this water is from overcharging, I am thinking maybe I should just run the charger one or two days of the week.* Otherwise is there an adjustment to the charger?
Water on top of a battery is from "boiling" the batteries, aka overcharging, or charging at too high a rate. The best cure for this is to use a so-called "smart" charger which usually has three stages. First stage is a high rate of charge, then as the battery nears full charge, the charger drops to a medium rate of charge. Finally, when the battery is fully charged, the charger drops to a "float" charge which holds the battery at full charge without overcharging it.

The advantage of having the charger on all the time is that if the boat should start to take on water for some reason, the charger will allow the bilge pump to continue running until--- or hopefully until--- someone checks on the boat. If the charger is off and the bilge pump starts cycling to take care of a leak, the pump could run the battery down at which point nothing will be evacuating the water out of the boat.

When we bought out boat it still had its original 1973 charger. This was a multi-selection charger--- you could manually select the rate of charge--- but it would not change rates on its own. Even at the lowest setting it was "boiling" the batteries, the pooling of water you have noticed on your boat. So we changed it out for an inverter/smart charger and have had no water on top of the batteries since.
Batteries still are basic 1890 tech , but the chargers have come a long way in the past 30-40 years.

The big question is (as usual) stand alone for better redundancy, or part of a system?

If the vessels inverter loads are minor , TV , house fridge or radar oven , a small cheapo inverter will work just fine. So a stand alone charger would be great.

If the inverter is a quality sine wave unit ,system designed to work with with a smaller noisemaker (best efficiency) the built in charger would be simplest choice.
It is not uncommon that older (crud building up on the bottom) batteries will spit goo even with a good ( made in the past decade) charger. One of my 8Ds* started misbehaving after 4 years. A new battery cured the puddles and other maladies. Also overfilling can lead to puddles.*Sitting creates small puddles at times for my house banks, but nary a drop on our on our 3 month summer cruise.
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